1. Field of the Invention
The present invention relates to a magnetic recording medium, such as a floppy disk, and, more specifically, to a disk provided with servo patterns for high-density recording and a method of recording such servo patterns.
2. Description of the Related Art
A floppy disk provided with servo patterns previously recorded on narrow tracks is used as a recording medium for the high-density recording of signals. FIG. 5A is a typical plan view of servo patterns recorded on such a disk, FIG. 5B is an enlarged plan view of portion Zz in FIG. 5A, and FIG. 3 is a plan view of a section of a floppy disk D. The both sides of the disk D shown in FIG. 3 serve as recording surfaces. According to standards, each of the recording surfaces of the disk D is divided into an innermost annular region of a width equal to R2-R1serving as a first nondata zone 1, an outermost annular region of a width equal to R4-R3 serving as a second nondata zone 2, and an intermediate annular region between the first nondata zone 1 and the second nondata zone 2 of a width equal to R3-R2 serving as a data zone 3.
As shown in FIG. 5A, servo patterns are formed in the data zone 3. The servo patterns are recorded at a plurality of positions on the disk D in a radial arrangement. Generally, the servo patterns are recorded while the disk D is rotated at a fixed rotating speed. Accordingly, portions of the servo patterns arranged in a radial arrangement near the outer circumference of the disk D are wider than those of the servo patterns arranged in a radial arrangement near the inner circumference of the disk D.
As shown in FIG. 5B, the servo pattern comprises servo information M and an A burst A(k) (k=2, 4, . . . , 2n) or a B burst B(k) (k=1, 3, . . . , 2n+1) following the servo information M.
The servo patterns are formed in concentric circles along the center lines O.sub.x (x=1, 2, . . . , n) of tracks. The distance between the adjacent center lines ox is equal to a tack pitch Tp on the order of, for example, 10 .mu.m. The inner edge E.sub.in of the A burst A (2) and the outer edge E.sub.out of the B burst B (1) coincide with the center line O1. The outer edge E.sub.out of the A burst A(2) and the inner edge E.sub.in of the B burst B(3) coincide with the center line O.sub.2. The servo information M includes servo preamble, a servo address mark and a servo address (gray code) recorded in succession. For example, servo information M includes an index signal in a servo pattern at one or a plurality of positions on one circle.
When the disk D is loaded into a disk drive for recording or reproducing, a magnetic head unit Ha reads the servo information M. When the servo information M is read it is recognized that the servo information M is followed by an A burst and a B burst. The scanning position of the magnetic head unit Ha is controlled so that the level of an output provided by a read head Hr included in the magnetic head unit Ha when the A burst is reproduced and the level of an output provided by the read head Hr when the B burst is read are equal to each other, and the magnetic head unit Ha is controlled for tracking so that the center of the magnetic gap of the read head Hr move on the center line O.sub.x of the track.
When the read head Hr leaves a data zone 3 and moves into a first nondata zone 1 or a second nondata zone 2 on a disk provided with servo patterns only in the data zones 3, the servo control of the read head Hr for tracking become impossible. For example, the position of the read head Hr become uncontrollable if the read head Hr leaves the data zone 3 and goes into the first nondata zone 1 during a data searching operation. In such a case, the magnetic head unit Ha moves suddenly to a waiting position over the periphery of the disk at a high speed, and stops with shocks at a position corresponding to the outer circumference of the disk. Such shocks may possibly damage the read head Hr and cause associated mechanisms to malfunction. Servo patterns are written to part of the nondata zones 1 and 2 so as to extend into the data zone 3 to avoid such a trouble.
However, since the disk to which the servo patterns are to be written is intended for high-density recording and the track pitch Tp is very small, a servo pattern recording process requires a very long time if the servo patterns are recorded at the track pitch Tp in a wide range in the nondata zone.